1. Field
The present disclosure relates generally to communication systems, integrated circuit (IC) design, and more particularly, to an apparatus (e.g., receiver) and method for filtering blockers and transmitter leakage while supporting carrier aggregation.
2. Background
A wireless device (e.g., a cellular phone or a smartphone) may transmit and receive data for two-way communication with a wireless communication system. The wireless device may include a transmitter for data transmission and a receiver for data reception. For data transmission, the transmitter may modulate a transmit local oscillator (LO) signal with data to obtain a modulated radio frequency (RF) signal, amplify the modulated RF signal to obtain an output RF signal having the desired output power level, and transmit the output RF signal via an antenna to a base station. For data reception, the receiver may obtain a received RF signal via the antenna, downconvert the received RF signal with a receive LO signal, and process the downconverted signal to recover data sent by the base station.
The wireless device may include one or more oscillators to generate one or more oscillator signals at one or more desired frequencies. The oscillator signal(s) may be used to generate the transmit LO signal for the transmitter and the receive LO signal for the receiver. The oscillator(s) may be required to generate the oscillator signal(s) to meet the requirements of the wireless communication system with which the wireless device communicates. The transmitter and the receiver local oscillators may be used to transmit and receive more than one RF signal at the same time.
For a full-duplex wireless device that can simultaneously transmit and receive data, circuitry within the receiver may observe interference from the transmitter. For example, a portion of the transmit signal may leak from a duplexer to the receiver, and the leaked signal (which is commonly referred to as a transmit (TX) leakage signal) may cause interference to a desired signal within the received signal. Since the transmit signal and the desired signal typically reside in two different frequency bands, the TX leakage signal can normally be filtered and typically does not pose a problem in itself. However, the TX leakage signal may interact with a jammer to generate cross modulation distortion components on both sides of the jammer. A jammer is a large amplitude undesired signal that is close in frequency to a desired signal. Some distortion components from the interaction between the TX leakage signal and the jammer may fall within the signal band of the desired signal and would not be filtered out. These distortion components would act as additional noise that may degrade performance. Furthermore, the TX leakage signal may go through a downconverter in the receiver and cause second-order distortion, which is proportional to the square of the TX leakage signal power. The effect of transmitter leakage in carrier aggregation receivers can be more significant. For example, multiple transmitters may exist. Thus, the intermodulation of the transmitter leakage and the local oscillators and their harmonics in a receiver chain, may result in in-band distortion in one of the receiver chains. Accordingly, there is a need for techniques to mitigate the deleterious effects of a TX leakage signal in a wireless device, and specifically in carrier aggregation receivers.
In TDD systems, there may be no TX interference for a receiver, but the same challenge still exists when multiple jammer and blocker signals are present at the input of the receiver. The resulting distortion may land in-band for a desired RF signal. In carrier aggregation, where multiple receiving channels exist, the intermodulation of the jammers with the receiver chain local oscillators may cause distortion for any of the desired receiving paths. Therefore, for TDD systems employing carrier aggregation, there is a need for techniques to suppress jammer signals in a wireless device.